Crispy shutters won't effect engine temp. There job is to stop water from surging back into the exhaust. How lucky you are is something no one can predict...
That's ingenious! how did you determine the lever arm length, it seems like you replicated the outdrive in the engine bay.. I suspect you made those easy to remove for access underneath..LOL
If I saw that I would take the water input hose off the thermostat housing And back flush, also open the thermostat housing and check. Those bits of impeller could lodge anywhere.. probably got caught in the steering cooler..